In most rotors or stators based on permanent magnets, the magnets are annular and have cylindrically shaped inner and outer faces which usually form complete coaxial cylinders, but occasionally the magnets are segmented. In the former case, the annular magnet is magnetized to have at an air gap alternating north and south poles extending across its working face. In the latter case, the magnet segments are usually magnetized to have one pole extending completely across the working face of each segment and the opposite pole extending completely across each working face of adjacent segments. See "Permanent Magnet Motors, Generators and Alternators" by James B. Gollhardt, Publication SPF5 of Allen-Bradley, Magnetics Division, Shawnee, OK, dated September 1983, which in FIG. 1 shows a motor component comprising two permanent magnet segments, each magnetized to have one pole extending across a working face at an air gap; in FIGS. 20 and 22, motor components having 2, 4, 8 and 12 magnet segments, each magnetized to have one pole across its working face at an air gap; and in FIG. 6, several permanent magnets, one of which forms a complete cylinder and typically would be magnetized to have one north and one south pole, each extending across 180.degree. of its working face at an air gap.
U.S. Pat. No. 3,231,770 (Hyde) shows in FIG. 8 a flexible permanent magnet strip 22 which is bent to form a complete cylinder as seen in FIGS. 4 and 5 and is magnetized to have a large number of alternating north and south poles extending across its working face at an air gap.
A few rotors or stators which have planar air gaps employ permanent magnets, the working faces of which lie in planes. For example, see "DC Motors", 5th Ed., 1980, an engineering handbook of Electro-Craft Corp., Hopkins, MN, FIG. 2.8.1 of which shows a pair of stators, each having eight cylindrical permanent magnets, each having a flat working face at an air gap. Although not disclosed, it is understood that the working faces of adjacent magnets have alternating north and south poles. The stator of the dynamoelectric machine shown in FIGS. 1-4 of U.S. Pat. No. 3,144,574 (Henry-Baudot) also employs a plurality of cylindrical magnets, each provided with a pole piece in the form of a sector of an annulus, which in effect displaces to an air gap the working face of its magnet (col. 2, lines 21-25).